. Biology of Reproduction, lecture on Reproductive Cycling

Biology of Reproduction

Fall 1998

text: Human Reproductive Biology 2nd Edition - R.E. Jones: Read pages 65-68 for this lecture

XIII. Reproductive Cycling                      back to XII. Puberty

	A. during Puberty the neuroendocrine regulatory mechanisms
	    necessary for female cyclicity develop

	B. Periodic fertility 

		1. pattern and rough timing regulated by biological rhythms

			a. suprachiasmatic nucleus (hypothalamus) generates
			   circadian (about a day) pattern in mammals

			b. in many species female and male reproductive
			   activity is circannual

				i. ovarian and testicular size and activity are
				   reduced (quiescent) most of the year

					(1) reduces energy expended maintaining ovaries

						(a) vitellogenin for yolk is energy rich

			c. other important rhythms for reproduction include:
			   circalunar, circatidal, ultradian (= pulsatile for hormones)

		2. pattern and rough timing are also regulated
		    by reproductive physiology 

			a. negative and positive feedback

			b. copulation, pregnancy & lactation

		3. environmental stimuli, from seasonal variations,
		   adjusts timing

			a. zeitgeibers entrain rhythms

			b. light - especially in birds, mammals and reptiles

				i. direct optic innervation of SCN
				   (retino-hypothalamic tract = Glu)

					(1) SCN is a part of the hypothalamic region (APS)
					   which stimulates GnRH and LH surges

					(2) SCN also projects to the pineal

				ii. some reptiles have a 3rd eye (= parietal eye) with
				   direct innervation of the pineal gland 

				iii.  pineal secretes melatonin
				     during scotophase (darkness )

					(1) helps coordinate rhythms

					(2) inhibits reproduction

						(a) scotophase is longest
					        during non-reproductive seasons

			c. temperature

				i. poikilotherms often require warmer temperatures
				   for gonadal recrudescence (growth and activation)

			d. food/water/shelter

			e. tides

				i. many fishes and invertebrates have reproduction
				   tied to the tides

					(1) they may also have
					    circannual reproductive rhythms

			f. social environment

				i. protandrous sequential hermaphrodites may depend
				   on group zoography to become female

C. Reproductive cyclicity is the neural integration of
   biological clock, reproductive physiology

		1. rhythms may be set in utero

			a. affected by hormonal rhythmicity

		2. rhythms set hormonal patterns

		3. hormones (as neuromodulators) modify rhythms via feedback

		4. environmental cues influence rhythms and hormone secretion

			a. neurally mediated

		5. hypothalamus, limbic system, & senses
		   are all reciprocally innervated

	D. Seasonal cycles coordinates male and female effort
	   at  times which  ­  fitness

XIV. Estrous Cycles